With the development of technology and the time, in order to meet user convenience, it is needed to configure a battery having the large capacity within a portable device such as a smart phone device or a tablet device. The battery having the large capacity usually means that it consumes longer charging time especially when a small charging current such as 1 A is used. Accordingly, a large charging current is usually employed by a conventional charger/adaptor device so as to reduce the longer charging time as far as possible. However, in some situations that cable lines losses exist or a large voltage variation is introduced to the input voltage, even though the conventional charger/adaptor device is originally designed to provide a maximum rated large current for battery charging, the conventional charger/adaptor device still outputs/provides a small charging current and cannot provide the rated large current for a battery. Thus, it is important to provide a novel charger device still capable of outputting a large charging current for a battery to effectively reduce the longer charging time even though this charger device is in the above-mentioned situations.